The present invention relates generally to radially expandable tubular grafts which are resistant to longitudinal compression resulting from an axially applied external force, and is resistant to axial shrinkage or axial foreshortening upon radial expansion. More particularly, the present invention relates to a microporous polytetrafluoroethylene ("PTFE") endovascular graft which has a reinforcing structure integral with or bound to the graft which permits radial expansion of the graft and stabilizes the graft against axial shrinkage upon radial expansion of the graft. Resistance to axial shrinkage is particularly desirable where a vascular graft is mounted onto a radially expandable endoluminal stent or alone onto an expansion balloon for intraluminal delivery and radial expansion.
The term "longitudinal compression" means a reduction in a longitudinal dimension resulting from an axially applied external force.
Radially expandable stents are used to maintain an occluded anatomical passageway in an unoccluded state. For example, the use of radially expandable stents in endovascular applications is well known, as exemplified by U.S. Pat. Nos. 4,733,665, 4,739,762, 4,776,337, and 4,793,348 relating to balloon expandable endoluminal stents, all issued to Palmaz, et al., U.S. Pat. Nos. 4,580,568, 4,800,882, 4,907,336, 5,035,706, 5,041,126, and 5,282,824 relating to balloon expandable and self-expanding endoluminal stents, all issued to Gianturco, et al., all of which are hereby incorporated by reference for the purpose of exemplifying stent types useful with the longitudinally reinforced grafts of the present invention.
The use of radially expansible stents is not, however, limited to endovascular applications. Rather, various types of endoluminal stents are also employed to maintain other anatomical passageways, such as biliary ducts and ureters in an unoccluded condition. In those uses where it may be desirable to cover the stent with a biocompatible material, particularly one which will promote tissue ingrowth, such as PTFE, the stent is covered with the biocompatible material. In the endovascular interventional medical field, endovascular stents may be covered by co-axially disposing a tubular PTFE vascular graft over an endovascular stent, the stent-graft assembly is introduced endovascularly and delivered to the desired location, whereupon the stent-graft assembly is radially expanded, such as by balloon dilatation to secure the stent-graft assembly against the vessel walls.
Balloon expansion of the stent-graft assembly occurs at pressures sufficient to cause both the stent and the graft to radially expand. As used herein, the terms "axial shrinkage" and "axial foreshortening" are used interchangeably to describe a reduction in the longitudinal length of the graft alone or the graft relative to the longitudinal length of the stent which occurs upon radial expansion of the graft or the graft-stent combination. Axial shrinkage of the graft relative to the associated stent typically results in exposure of the proximal and/or distal end of the stent. Such exposure may, in turn, provide a fluid passageway for body fluids, such as blood, to flow between the abluminal wall of the graft and the luminal wall of the anatomical passageway, e.g., a blood vessel. Such an escaping flow as in, for example, an arterio-venous fistula repair, is undesirable and may be associated with increased mortality and decreased patency of the graft or stent-graft. It is desirable, therefore, to provide a tubular PTFE structure which is resistant to axial shrinkage during radial expansion of the PTFE structure.